An oxyalkylene polymer which contains a silicon-containing group having a hydroxyl group and/or a hydrolyzable group bound to a silicon atom and capable of crosslinking through the formation of a siloxane bond, which will be simply called a reactive silicon
group hereinafter, is disclosed in, for example, JP-A-52-73998 (the term of "JP-A" herein means unexamined Japanese patent application). A typical example thereof is a polymer represented by the following general formula: EQU X'.sub.3 Si (oxypropylene polymer) SiX'.sub.3
wherein X' represents a hydrolyzable group such as a methoxy group.
Similar to a room temperature curing silicon rubber, an oxyalkylene polymer containing a reactive silicon group crosslinks through the formation of a siloxane bond (Si--O--Si) between polymer molecules at room temperature under the effects of, for example, moisture in the atmosphere, thus giving a rubber-like cured material. The cured material thus obtained, which is excellent in, for example, stretching properties and strength, is widely used for various purposes, e.g., in sealants and adhesives.
The surface of the cured material is frequently coated. It is one of the advantages of this cured material that it can be coated with almost any paint commonly used in coating cured materials, different from room temperature curing silicone rubbers, since the main chain of the former material comprises the oxyalkylene polymer. In the case of a silicone rubber, on the other hand, the water and oil repellent surface cannot be coated with any paint in practice.
An oxyalkylene polymer containing a reactive silicon group is frequently used together with a plasticizer. When the plasticizer is a low molecular weight one commonly used in the art, however, an alkyd paint applied on the cured polymer shows poor drying characteristics, though coating is not impossible. Therefore it is difficult in practice to coat the cured material with an alkyd paint. Accordingly it is almost impossible to coat a cured oxyalkylene polymer, which is used together with a low molecular weight plasticizer, with an alkyd paint.
A plasticizer is conveniently used to lower the viscosity of a composition and to thereby improve the workability or to improve the tensile properties of a cured material. Accordingly the inventors have attempted to find a plasticizer which will not affect negatively the drying characteristics of an alkyd paint. As a result, the inventors previously found that the abovementioned problem can be solved by utilizing a so-called high molecular weight plasticizer.
However a cured material wherein a high molecular weight plasticizer is used has a disadvantageously high modulus. Although the modulus can be lowered by adding a large amount of the plasticizer, the resulting material becomes poor in the tensile properties and stretching properties. It is desirable to readily control the modulus, which is one of important characteristics, of a rubber material without affecting negatively any of the other characteristics of the same.